1) We only invited my kids' friends of whom they wanted to invite. We as parents, told our kids how many we can invite. And per budget.
Never invited the whole class. Teachers, have a "rule" that any invitations are to be given to them, and THEY will disperse the invitations, discreetly to the child/the parent, in their cubby or going home folder.
Or yes, mail if if you can.
2) Per party guests and wording of invitations: All of my friends including myself, word the invitations as such: "Sally & 1 parent, is invited to Erica's 5th Birthday party. It is a drop-off party or the parent may stay." (in your case, say that it is NOT a drop-off party).
It is worded this way, so that the invitation clearly states, the the invited child and ONE parent, is invited. Otherwise, you will get a whole truckload of others to your party. I have seen, parents bring their invited child... in addition to their other kids and/or an Aunty or other relatives and the Dad or grandparent.
For me: I only invite the child and ONE parent to my kids' party. It is my child's party. Not a venue for everyone. And simply put, we have a budget. We cannot possibly, feed EVERYONE and their relatives nor entire family. It is a kid's party for the birthday child. And goody bags are for the children that are invited.... ie: my child's friends.
I and my friends, always send out invitations at least 3-4 weeks ahead of time. SO that, each family/parent, can plan ahead. And decide who will attend the party. Families are busy need to know ahead of time when a party is so that they can plan their schedules, too.
3) Simply state, "this is not a drop-off party. 1 parent will need to attend and assist their child. We do not have enough Adults to supervise the pool party."
4) My daughter would like to gift a local animal shelter, in lieu of gifts. If you would like to, the animal shelter accepts dog/cat food, small toys, old blankets, etc. Our Family, will deliver these items to the shelter for you. (other wise the invited may thing that THEY have to take things to the shelter themselves.) Being this is a party for your child, then you should have the guests bring those items to your home... for YOU to then deliver to the shelter.
Know that, not everyone may participate in donating things. Or they might. It depends on if they want to. That is the point. It should be voluntary.
BUT, as with any "donations"... will the people contributing... get a RECEIPT for it, for their tax purposes??? How will they get one?
You would need to write down a list of people who donated for your daughter's Birthday Party... and what they donated or how much. IF a parent should ask, about donation receipts, for their taxes. You have to anticipate... such questions.
5) Per RSVP's. State a deadline to RSVP by because you need a head count... as well as stating your phone contact number and an e-mail address.